Researchers from the Royal Botanic Gardens, Kew, Forest Research and other collaborators have published a new study in Nature Communications detailing the first-ever European ash (Fraxinus excelsior) pangenome, using high-quality DNA to aid research into natural ash dieback resistance.
Using the pangenome, constructed from a group of 50 trees of diverse origins, the scientists analysed a genomic dataset from more than 1,000 trees to identify genes associated with resistance. They found 211 genes with possible links to ash dieback resistance, 16 of which were dispensable, meaning they were only present in some individual trees and not across the board.
"Unlike genes found in every individual of a species, dispensable genes are not always essential. They may however confer traits advantageous in certain contexts, like disease resistance or better drought tolerance, potentially allowing populations to adapt more quickly to changing circumstances," writes Kew.
Ash dieback is a major concern for the UK and has decimated British treescapes since first being detected in 2012, killing off millions of trees. Only a tiny proportion of trees (as low as 0.5%) remain healthy after long-term disease exposure.
Pangenomes provide a more comprehensive way of studying susceptibility to pathogens, compared with using a single genome, as they capture the dispensable DNA sequences carried by some trees but not others. The pangenome constructed in the recent study was 22% larger than a high-quality genome from a single ash individual, when accounting for dispensable genetic sequences.
Dr Daniel Wood, Kew research fellow and first author, comments:
"If each ash genome is the same movie, these findings highlight how many director’s cuts, extended editions, deleted scenes and alternate endings nevertheless exist in wild populations – perhaps most of the runtime is the same, but the variable bits can potentially make the difference between a box office smash and a flop. Using the total catalogue of genetic sequences, represented in the pangenome, we identified genes potentially associated with resistance to ash dieback. However, this resource can be applied to identify the genetic basis of other traits of interest, such as environmental resilience, or resistance to other threats such as the emerald ash borer beetle."
Dr Laura Kelly, research leader, also comments:
"The pangenome provides a powerful new tool in the continued fight against ash dieback, and in the response to the ever-growing threat from the emerald ash borer as its invasion advances across Europe."
Amongst the 50 sampled trees was a young ash specimen grown at Kew Gardens in London, as well as trees sampled from a Forest Research trial site outside Norwich. DNA was also collected from private land and Paradise Wood in Oxfordshire, which is a site owned by the charity Earth Trust.
The ash trees of non-UK provenance were all grown at Paradise Wood from seed collected from a wide variety of locations in Europe for the Realising Ash's Potential Trial.
The findings are an output of the Centre for Forest Protection (CFP), a joint venture between Kew and Forest Research (the research agency of the Forestry Commission), funded and managed by the Department for Environment Food and Rural Affairs (Defra). The CFP brings together UK and international expertise to foster research supporting the health, resilience and future of the UK’s forests and woodlands."
The research can be found here.
